Process of dewaxing petroleum oils and the like



Feb. 2, 1954 E, PALMQVIST 2,668,141

PROCESS OF DEWAXING PETROLEUM on. AND THE LIKE File d Nov; 19. 1948 Aux/Mary liyu/d I? My I sa/qf/on Aux/wary d wax Dewaxd oil I lnvenfor 5-9097)? Eon or Emanu/ ahrqw'sf Patented Feb. 2, 1954 PROCESS OF DEWAXING PETROLEUM OILS I AND THE LIKE Fredrik Teodor Emanuel Palmqvist, Stockholm, Sweden, assignor to Aktiebolaget Separator- Nobel, Sweden Stockhohn, Sweden, a corporation of Application November 19, 1948, Serial 61,032 16Claims. (01. 196-19) This inventionrelates to the dewaxing of pe- H troleum oils, shale oils, tars, and the like, and more particularly to an improved dewaxing process in which oil losses incident; to removal of the Wax are reduced.

Dewaxing is one of the most important steps in the production of lubricating oils, transformer oils, switch oils, etc., from petroleum oils, shale oils, tars or their fractions and residues. By removing such paraflinic hydrocarbons as precipitate at low temperature, the pour point and the cloud point of the oil is lowered so that it can be used for lubricating, insulating, chilling, etc., at low temperatures.

Low viscosity oils can easily be dewaxedby chilling to a temperature at which the paraflinic hydrocarbons precipitate in the form of solid crystals removable from the liquid hydrocarbons by filtration. Highly viscous'oils, on the other hand, cannot be dewaxed in the same simple way but must be mixed with a suitable diluent or solvent in order to reduce the viscosity at low temperature and thus permit a satisfactory'ra'te of separation of the wax. At the dewaxing tem-' perature, the solvent should have a high solvent power for the oil and a low solvent power. for

'etc.; mixtures of ketones such as acetone or methyl ethyl ketone, with'aromatic hydrocar bons such as benzolor toluol; chlorinated 'hydrocarbons such as ethylene dichloride per se or mixed with arom'atic'hydrocarbons such as benzol.

Generally the'wax-bearing oil is mixed with the solvent at increased temperature, whereupon the solution is chilled to a temperature at which all or most of the Wax is precipitated. The wax is then removed by settling, filtration or centr'ifuging, and the solvent is recovered from the oil and wax by distillation.

In this way, oil having the desire'dpour point is obtained and also a wax cake containing a v certain amount of oil which not only represents a loss of valuable oil but also reduces the melt-'- ing point of the wax and thus its sales value,

the solid wax to be removed. With certain sol- V vents and solvent mixtures, the difference in sol vent power for oil and wax is so great that the solvents not only act as viscosity reducers but also as wax precipitators. to advantage for low viscosity oils as well. I

Generally, the difference in solvent power for wax and oil increases with reduced temperature, and the higherthe temperature at which this difference is noticeable, the higher is the tem-' perature at which the dewaxing can take place. Since the economy of the dewaxing process depends mainly on the amount of chilling required, a solvent should be used which gives the smallest possible spread, that is, the smallest possible Such solvents may be used difierence between the dewaxing temperature and the desired pour point of the oil. v

The solvent should also be chemically stable; easy to recover, non-corrosive and non-poisonous; Furthermore, it should be easily miscible'with .oil

at low temperature, and the viscosity of'themix- 3 time should be low, so that uneconomically large quantities of solvent need not be used in order to render the wax easily separable by mechanical means. g The above-mentioned conditions are fulfilled by a great number of solvents widely used in the petroleum industry. Such solvents are, for instance, -parafilnic hydrocarbons with low boiling point -such 'as' propane,

hexane; light naphtha-,

the latter increasing in nearly geometrical pro-v gression with decreasing oil content and increjas ing melting point.

In order to improve the yield of dewaxed oil and the quality of the wax, the latter is generally deoiled further by being washed with the same solvent as used in the dewaxing process. I When the wax is removed by'filtration, this deoilingis often carried out by sprinkling the wax cake with freshsolvent; and When centrifugation is used to remove the wax, the latter is mixed with fresh solvent and centrifuged again. These methods have, however, the disadvantage that the quantity of solvent circulating through the system is considerably larger than the quantity of solventre quired for the dewaxing only. The quantity of solvent used for deoiling the wax may be twice as great as the the washing liquid entirely or partially to the process involves a considerable complication since it must be carried out in at least two steps and requires an installation with a relatively large liquid volume, as well as accurate flowand tem; perature control of the liquids fiowingpartially in countercurrent and through heat exchangers.

The present invention has for its principal ob ject the provision of a process by which the' oil losses with the wax can be reduced in a simpler and cheaper way than described above. The process comprises essentially a centrifugation of the oil, in whichprecipitated wax is brought'into contact with an auxiliary liquid having an inter face tension in relation to the oil solution of less than 50-dyn. /cm., thus-displacing the oil solution 7 oil" ntentof-about45%.

from the separated wax so that the latter is discharged from the separator bowl or centrifuging locus in a relatively oil-free state.

The process can be used to advantage for detr m a s o s ve a ng ei h r a o e or a higher specific gravity than the wax to be removed, but in either case the auxiliary liquid has a specific gravity intermediate the specific gravities of the oil solution and the wax. In the first case, the auxiliary liquid must have a higher specific gravity than the oil solution, while in the latter case the auxiliary liquid? light; er than the oil solution. In both cases, it is ad visable to discharge the auxiliary liquid entirely or partially together with the wax.

Using the same quantity of solyent as otherwise required for the dewaxing step only, it, possible to obtain by this single-stage combined dewaxing and deoiling process a higher yield of dewaxe'dbil and awax'containingless oil, with considerably lessv consumption of power and steam for and solvent recovery, than with the aiormentionedprioimethods. If. for example, an oil containing 25%wa'x is diluted with 200% by. weight of light, naphtha, followed by chilling to 28 C. and centrifuging without any. auxiliary liquidfihe yield is about 55% lubricating on with a our point of C. and 45% wax with'an The same result is obtamed by. vacuum or". pressure. filtration. Howeyerfif the centrifugat'ion 'is' carried out in'the presence of a suitable auxiliary liquid according tb the. invention, about 72% 'oil'with a pour point of %l5f. C. and'28% wax with an 'oil content of only about 101% are obtained at the same rate dfcentrifugation. When filtering, or when centrifugin'g without any auxiliary liquid, at least t l 6.. steps and 400% solvent would be required iii-order to obtain the same result;

I The use of certain, auxiliary liquids in connection Withcentrifugation has previously been proposed, In, those prior'cases, however, the auxiliary liquids are not of a character such that th yi are efiective to displace oil from the wax Separated the. centrifugal bowl. On the, contrary, they act merely as carrier. liquids; that is, theyj'havejsuch a high surface tension and. specifi'e. gravity that the separated waxjretains the deduced oil and is carried on the surface of the quidli'ri the same way "as metal chips on inercury. As suchoarrier'liquids, more. or less corrcentrated solutions of inorganic salts in water, glyeri rie, etc., have been proposed.

'Tl-ie'char'acteristics of the auxiliary liquid to be used according to: this invention differ in prineit emfsejvgmi respects from the so-called carrier. liquids previously proposed, and, should meet the following requirements:

1. The. interface tension in relation tov the oil solution should not exceed about 50 dyn./cm., so that the wax crystals can pass in contact with the auxiliary liquid as single particles and not as crystal agglomerates occluding large quantitl'ie auxiliary liquid should not have any essential uence on ity, the specific gravity of the auxiliary liquid solution and equal to or lower thanjthato'f the ties of oil. I

w I a the interface tension.

should. be equal to or higher. than that of the oil was.

Minor changes of the composition of Whenusing solvents withlow specific grav 3'IWhen using solvents with high specific gravm. re fi av y of th aux l ar iquid solution and equal to or higher than that of the wax.

4. The auxiliary liquid should be practically insoluble in the oil solution and easy to recover y h n h lin ti lat on. ad on of inert substances, etc.

5. The auxiliary liquid should be miscible with water or other substances so that its physical properties can be adjusted according to the changes of the physical properties of the oil and the wax caused by variations of temperature, etc.

Examples" oi suitable auxiliary liquids are: aqueous ketones such as acetone, methyl ethyl ketone, diethyl ketone, etc., esters, nitro-, aminoor halogen-substituted aliphatic and aromatic substances, etc., especially those of typically polar nature, or mixtures of these substances, also with the addition of alcohols.

previously mentioned, the dewaxing in the presence. of an auxiliary liquid. is preferably carried out by the action of centrifugal force.' The waxvbearing oil is mixed with a suitable solvent and the wax is precipitated by chilling. if the specific, gravity of the solvent is lower than that of the. wax, the mixture is centrifuged in a cylindrical o conical centrifugal bowl at the. periphery of which one or several wax discharge'openings or nozzles are arranged. The auxiliary liquid is fed to the centrifugal bowl simultaneously with thewaxy oil solution, preferably through a concentrical inlet conducting the auxiliary liquid separately to the periphery of the bowlin crucif avoid emulsification of the oil solution and the auxiliaryi u dh a b w s s n 9 a ample, in British Patent No. 10.314 of race. The dew'axed oil solution is discharged through the central part of the centrifugal bowl, whereas the Separated wax, together with thefauxiliary liquid, lea th w hro h p n s a th re riphery.

m h d w e 011 l 9 lh- Q YQ recovered in the conventional way by distilla; en- T was is e ara e -iro new m s y m ans. o asu in am is. ii iq l s r c n a t etc s l arati s by e ns i ea i myq i s s ci l adramasss sih ih fm t q a v se ra e q i t e y-w m: hea a l sr i a. he h fl nasll also, be carried. ou'tin different steps. as the usual waxswealf g D 929 .5, the waxes with, me gs? bei m x s n qu d late wi h i i a qi em s t siwes swh i i erise r i d 1 r. as as o s al: u sl r his ii plus -maw se i si i ev eqrder h mac i aux! da as in ea ed Q-Su h. empera-'- ture e as ssues and t ees ia u i then e n r dual re u e hat a 'fir' t ha was w th; r l n p int are precipitatedan'd separated, followed by pre; cipitation and epa atesbf e eawater; gradually decreasing melting point. The, auxa mm s' fii a ii e est d: w. e me s s a Wax-freestate.

Whenfractionating thewax. in thepr-esence of an auxiliary quid, the'latterssolvent, cr m ompbii i s. tan be are a ig td in t e aux l a nuisis uch awe-fi s and, if desired, by changing the temperature at the, sametime. Ecpthispurpose I. prefer to use q dsw i ,w c n ne sst nd-wi hout.d gcu tx from the main, auxiliary liquid, for by; aze ro ic di t l a on, etc. w ereby; a. red al-'1 atiqnof; he-wholeau iarxli u dlmixtu elcau snoumbe equalto or lower than that of the oil b voided,

Sometimes it maybe advisable to carry out the dewaxing or deoiling procedures, or both, in several steps. The wax concentrate from the first step is centrifuged in a second step, preferably after further addition of solvent, using auxiliary liquid in both steps. It is also possible to exclude the auxiliary liquid, for instance in the first step, and to mix the wax concentrate with auxiliary liquid before it is centrifuged in the next step. Under certain conditions it may be sufiicient to feed the wax concentrate from the first step directly into the second centrifuge bowl together with the auxiliary liquid.

As compared with the prior multi-stage methods, the process of the present invention has the separation of solid from liquid substances according to the invention may-also be used to advantage in other chemical and industrial processes within or outside the petroleum field, particularly when the problem is to separate, in a technically pure form, solid or semi-solid substances which are difiicult to filter, for instance organic or inorganic salts from viscous solutions, emulsions, etc.

In the accompanying drawing, the single illustration is a schematic view of an installation suitable for practicing the invention in the dewaxing of oils.

Wax-bearing oil and solvent are mixed in fixed proportions and the resulting solution is chilled to the desired dewaxing temperature in the cooler I, after which the separation is effected in centrifuge 2.

The solvent is then recovered from the oil solution obtained in the separation, by distillation in the distilling apparatus 3, and is returned to the process. Wax-free oil with the desired pour point is obtained from apparatus 3 as distillation residue. During the centrifuging, auxiliary liquid is fed from cooler 1 to the separator 2, the bowl of which may be provided with nozzles at the periphery, the auxiliary liquid preferably being introduced at the periphery of the bowl in front of the nozzles, as previously described. Part of the wax-bearing auxiliary liquid discharging from the separator bowl may be returned to the separator, as shown at 2a, if the wax content is not too high. The remaining portion, after being heated in the heater 4, is mixed with water or some other additive which reduces the solubility of the wax in the auxiliary liquid at high temperature, the solubility reducer being added through pipe 8. The resultmg two fluid phases are separated from one another in the separator 5, into an oil-poor wax containing small amounts of auxiliary liquid which may be driven off and returned to the system, and auxiliary liquid containing the added solubility reducer (for example, H) and small amounts of oil and wax. After distilling the auxiliary liquid in the distillation apparatus 6, the solubility reducer may be returned to the system through pipe 8. The recovered auxiliary liquid is likewise returned, after cooling in the cooler Small amounts of a wax-containing oil are obtained as balance from the apparatus '6', and this balance may be subject to'a repetition of the treatment to which the original wax-bearing oil is subjected.

The above procedure has been described only by way of example, and it will be understood that other embodiments are possible within the scope of the invention. I V

I claim: V

1. In the dewaxing of mineral oils, shale oils, tar oils, and their fractions and residues, by centrifuging the oil in the presence of an added oildissolving and wax-precipitating solvent,' said solvent forming with the oil an oil solution containing precipitated wax crystals, the process which comprises forming in the centrifuging locus, and adjacent the oil solution, a layer of an auxiliary liquid having a specific gravity inter; mediate the specific gravities of the oil solution and the wax, said auxiliary liquid being substantially insoluble in the oil solution and having a surface tension, relative to the oil solution, which is's'uificiently low to allow the wax to pass into said layer in the form of separate crystals while preventing penetration of oil into said layer, and, during the centrifuging operatiompassing wax crystals separately through the boundary surface between said oil solution and layer while displacing oil from the wax at said layer, thereby deoiling the wax in said locus.

2. The process according to claim 1, in which the specific gravity of the auxiliary liquid is higher than that of the oil solution but lower than that of the wax.

3. The process according to claim 1, in which the specific gravity of the auxiliary liquid is higher than that of the wax but lower than that of the oil solution.

4. The process according to claim 1, comprising also the step of adding water to the auxiliary liquid to adjust its interface tension to within the prescribed limit in relation to the oil solution, the auxiliary liquid being soluble in water.

5. The process according to claim 1, comprising also the step of adding water to the auxiliary liquid to adjust its specific gravity to an amount intermediate the specific gravities of the wax and the oil solution, the auxiliary liquid being soluble in water.

6. The process according to claim 1, comprising also the steps of continuously introducing the auxiliary liquid into the centrifuging locus, and

continuously discharging said liquid with separated wax through the outerperiphery of said 7 locus.

7. The process according to claim 1, in which the auxiliary liquid is introduced into the centrifuging locus outside the interfacial zone between the separated wax and the separated oil solution in said locus.

8. The process according to claim 1, comprising also the steps of discharging from the centrifuging locus a mixture of auxiliary liquid and wax, and fractionating said mixture by thermal treatment to separate the wax from the remaining oil.

9. The process according to claim 1, comprising also the steps of discharging from the centrifuging locus a mixture of auxiliary liquid and wax, separating the wax and remaining oil from said mixture, and subjecting said last wax and oil to further treatment to recover the oil from the wax.

10. The process according to claim '1. comprisalso the steps dischaif ilisf :the centriiuging; locus a mixture of auxiliary liquid and wax, adding a solubility reducer inKwhich the auxiliary liquid is soluble to said mixture to reduce the solubility of the waxin the liquid at bearing oil and an oil solvent to a centrifuging locus and there separatingthesameinto an oil solution and wax, contacting said Wax, while in said locus, with an auxiliary liquid substantially insoluble in the, oil solution and having an interfacial tension in relation to the oil solution of less, than 50 dyn./cm., said liquid having a specific gravity intermediate the specific gravities of'the wax and the oil solution, passing the wax through the boundary surface between the auxiliary liquid and'the oil solution in said locus, whereby said liquidtdispl'aces oil entrained in the separated wax, and discharging the wax and auxiliary liquid from the locus separately from the initially separated oil andsaid displaced oil. 12. The process according to claim 1, in which the auxiliary liquid is an aqueous ketonc.

13. The process according toclaim 1, in which the auxiliary-liquid is an ester.

14. The process according to claim 1, in which the auxiliary liquid is a substituted aliphatic compound.

15. The process according to claim 1, in which the auxiliary liquid is a substituted aromatic compound.

16. The process according to claim 1, in which the auxiliary liquid includes alcohol.

FREDRIK TEODOR EMANUEL PALMQVIST.

References Cited inthe file of this patent UNITED STATES PATENTS.

Number; Name Date 1,343,636: Livingstone Mar. 8, 1932 'l,9(il,2 4,0, Henriken Mar; 14, 1933 1;,938g545 Sullivan Dec; 5, 19.33 2,081A63- Lindgren May'25, 1937 2334,5116 Jones Mar. 11, 1941 2;;2-89A31 Jung July 14,, 19.42 2,343A59 Engel May 9, 1944 2,407,834 Jones Sept. 1'7, 1946 2,439,454 Lindgren c Apr. '13, 1948 

1. IN THE DEWAXING OF MINERAL OILS, SHALE OILS, TAR OILS, AND THEIR FRACTIONS AND RESIDUES, BY CENTRIFUGING THE OIL IN THE PRESENCE OF AN ADDED OILDISSOLVING AND WAX-PRECIPITATING SOLVENT, SAID SOLVENT FORMING WITH THE OIL AN OIL SOLUTION CONTAINING PRECIPITATED WAX CRYSTALS, THE PROCESS WHICH COMPRISES FORMING IN THE CENTRIFUGING LOCUS, AND ADJACENT THE OIL SOLUTION, A LAYER OF AN AUXILIARY LIQUID HAVING A SPECIFIC GRAVITY INTERMEDIATE THE SPECIFIC GRAVITIES OF THE OIL SOLUTION AND THE WAX, SAID AUXILIARY LIQUID BEING SUBSTANTIALLY INSOLUBLE IN THE OIL SOLUTION AND HAVING A SURFACE TENSION, RELATIVE TO THE OIL SOLUTION, WHICH IS SUFFICIENTLY LOW TO ALLOW THE WAX TO PASS INTO SAID LAYER IN THE FORM OF SEPARATE CRYSTALS WHILE PREVENTING PENETRATION OF OIL INTO SAID LAYER, AND DURING THE CENTRIFUGING OPERATION, PASSING WAX CRYSTALS SEPARATELY THROUGH THE BOUNDARY SURFACE BETWEEN SAID OIL SOLUTION AND LAYER WHILE DISPLACING OIL FROM THE WAX AT SAID LAYER, THEREBY DEOILING THE WAX IN SAID LOCUS. 